Metal deposition process and apparatus



April 1962 R. G. BOURDEAU 3,031,338

METAL DEPOSITION PROCESS AND APPARATUS Filed April 3, 1959 FIG. I

HEATER /50 ag PUMP H J VA POR AT TORN EYS United States Patent 3,031,339,v METAL DEPUSITION PROCE S AND APPARATUS Romeo G.-Bourdeau,'Brighton, Mass 'assignor to Alloyd Research Corporation, WatertoWn, Mass.,-a'corporation of Massachusetts :Filed Apr. 3, 1959, Ser. No.i80,874

S Cliaims. (Gl. 117-97) The present invention relates to metal deposition and,

more particularly, to coating the inner surfaces of long tubes with particular metals. Itis oftendesiredto coat the inner surface of a long tube wither-particular metal in order to impart predetermined physical, chemical and mechanical characteristics. Thus, for example, it may be desired to coat a steel or glasstube internally with a refractory metal. It has been proposed tocoat such'a tube internally by directing a vaporized compound of the metal through'the tube and decomposing or reducing'the vaporized compound atelevated temperature in orderto deposit the metal. However, in the past, such processes have resulted in the deposition of impure metal in forming the coating andin poor adhesion between the coating and the tube substrate apparently because of the deposit of alow quality powdery form of the metal on thetube substrate as the temperature rises prior to the depositof the high quality pure metal at the desired elevated temperature. This difliculty is especially important in the case of tubes-thatare extremely long in relation to their diameters.

Objects of the present invention are: to provide processes and devices for coating-the inner surface of a long tube by moving in one direction inside the tube a vapor, comprising a metal compound selected from the class consisting of carbonyls, organometallics, halides, combinations thereof and mixtures thereof, and moving in the opposite direction outside the tube a heating unit that generates a moving heat zone of restricted length'within the tube, the rate=of movement of the heating unit b eing' such as to deposit metal from a preselected p'ortion o f the vapor; and to provide processes and devices of the foregoing type wherein'a stationary heat zone of ei tended length fully encompasses the tube inorder to prevent condensation of the vapor in regions not subject to the moving heat-zone.

Other objects of the ,present invention will in part -be obvious and willin part appear hereinafter.

The invention accordingly comprises the process involving the several steps and .the relation and order'of one or more of such steps with respect tofleach ofthe others, and the apparatus possessing the construction, combination of elements and arrangements of parts, which are exemplified in the followingdetailed disclosure, and the scope or which will be indicated in the appended claims.

For a fuller understanding of the nature and objects of the present invention, reference should be had to the following detailed description taken in connection with the accompanying drawing wherein:

FIG. 1 is an exaggerated, fragmentary view of materials undergoing a process of the present invention; and

FIG. 2 is a schematic diagram of an apparatus for effecting a specific process of the present invention.

Generally, the process illustrated in FIG. 1 comprises coating the inner surface of a long tube It) by flowing in one direction within the tube a vapor 12 of a metal bearing material, maintaining the vapor at a given temperature and freely in contact with the tube substantially throughout its length as by means of a heating unit 14 of extended length, and moving in the opposite direc tion outside the tube a heating unit 16 that generates a moving heat zone of restricted length within the tube.

The arrangement is such that the temperature gradient in the vapor at the front ofthe moving heat zone is sufficiently steep to ensure that initially metal deposition occurs at a desirably high temperature. Thus, any'low quality metal deposited at'the rear of'the moving heat zone does not interfere with the bond between the coating already/formed and the tube substrate. This process is particularly adapted'for use where'the lengthof the tube is at least times its diameter. Thetube, for example, is composed of a metal, such as'stainless 1 steel or monel metal, or a fused inorganic material, such as glass or ceramic. Deposition may takeplaceby decomposition of the vapor at the elevated temperature or by reduction at theelevated temperature in the presenceof a reducing gas such as-hydrogen.

The metal bearing vapor has a-first component selected from the class consisting of the transition elements, the rare earth elements, the actinide elements and-combinations thereof, and a second component selected from th carbonyls, organics, halides and combinations thereof. Examples of the foregoing are ferric carbonyl, molybdenum carbonyl, nickel carbonyl, chromium chloride, tungsten chloride, molybdenum chloride, bis-cyclopentadienyl metals such as'bis-cyclopentadienyls of iron, manganese, cobalt, nickel, rhodium and vanadium, bis-cyclopentadienyl metal halides such as bis cyclopentadi'enyl chlorides, bromides and iodides of titanium, zirconium, hafnium, vanadium and "tantalum, cyclopentadienyl carbonyls such as cyclopentadienyl manganese tricarbonyl, bis-cyclopentadienyl metal carbonyls wherein themetal is molybdenum, tungsten or iron, dibenzene metals such as dibenzene compounds of chromium, molybdenum and vanadium and dibenzene metal halides such as dimesitylene' di-iodide.

As indicated above, the flow rate of vapor 12'and the speed of heat zone 16 are adjusted to produce a coating 18 on the inner surface of tube It of predeterminedly desired thickness' The heating zone ranges in temperature from 300 to 1000 C., the carbonyls and the organometallic compounds decomposing or undergoing oxidation reduction within the range of from 250 to 650 C. andthe halides decomposing or undergoing oxidationreduction within the range of from 650 to 1050" C. Insteadot a moving heat zone, a succession of stationary heat zones may be employed. The pressure of the metal containing vapors preferably ranges from .5 to 25 mm. of Hg and, when hydrogen is employed as a reduction gas, the total pressure of the vapor ranges from 5 to 50 mm. of Hg.v Preferably,.-the reducing gas is present in excess for the purpose of-ensuring that complete reduction occurs. The vapor maybe produced by heating the metal containing compounds in solid form.

An apparatus for plating the inner surface of a tube 20 in accordance with the present invention is shown in FEG. 2. At one end of the tube 20, a reducing gas and a metal containing vapor of the aforementioned type are introduced through a suitable seal 22 from supplies 24 and 26, respectively. The supply within container 26 is in the form of a powder, the vapor pressure of which is determined by a heater 28 that is kept at constant temperature by a control 30. At the other end of tube 26, exhaustion occurs through a seal 32 by a pump 34. Surrounding tube 20 throughout its length is a heating coil 36 that maintains the vapor from supply 26 in the gaseous phase and prevents any condensation on the inner surface of tube 20 by maintaining a uniformly elevated temperature. Surrounding tube 24 is a heating unit 38, which is carried by a dolly 40. Dolly at is adapted for reciprocal motion upon suitable rails 42. The motion of dolly 4%? is controlled by a chain 44 and a pair of sprockets 46 and 48, which are driven by an adjustable drive 50. his apparent that the rate of flow of gas from supply 26 may be determined by the temperature of heater 23 and the action of pump 34 and that the rate of movement of heater 38 is determined by adjustable drive 50.

Example In a specific example of the foregoing process effected by the above described apparatus, tube was 20 inches in length, had an external diameter of 7 mm. and an internal diameter of 5.0 mm. At one end of the tube, the vapor of molybdenum carbonyl, heated to approximately 90 C., and hydrogen, at approximately five times the pressure of the molybdenum carbonyl was introduced. The entire tube was heated to a temperature of approximately 90 C. At the other end of the tube exhaustion occurred in order to cause a flow rate of 20 mols per hour. The molar ratio of the vapor was 10% molybdenum carbonyl to 90% of hydrogen. The moving heat zone, at a temperature of approximately 450 C., was moved at a speed of approximately six inches per hour. The thickness of the high quality deposit produced on the surface of the tube was approximately .050 mm.

Since certain changes may be made in the above process and apparatus without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted in an illustrative and not in a limiting sense.

What is claimed is:

1. A process for coating the inside of an elongated tube section, said process comprising the steps of directing a mixture of a heat decomposable gaseous metal compound and an auxiliary gas through said tube from one end thereof to the other, heating the entire interior of said tube section in order to maintain said mixture in the gaseous phase at a predetermined temperature, said mixture being in contact with substantially all of the inner surface of said tube section, and moving a heat zone in the direction along said tube from said other end thereof to said one end thereof, said heat zone generating a temperature above the temperature at which said decomposable metal compound decomposes.

2. A process for coating the inside of an elongated tube section, said process comprising the steps of directing a mixture of a heat decomposable gaseous metal compound and an auxiliary gas through said tube section from one end thereof to the other, heating the entire interior of said tube in order to maintain said mixture in the gaseous phase at a predetermined temperature, said mixture being in contact with substantially all of the inner surface of said tube section, and moving a heat zone in the direction along said tube from said other end thereof to said one end thereof, said heat zone generating a temperature above the temperature at which said decomposable metal compound decomposes, said mixture being produced by contacting said auxiliary gas with said decomposable metal compound and introducing the resulting mixture into said one end of said tube section, and exhausting said other end of said tube section in order to maintain the pressure of the decomposable metal gaseous compound at between .5 to mm. Hg.

3. A process for coating the inside of an elongated tube, said process comprising the steps of directing a mixture of molybdenum carbonyl vapor and hydrogen through said tube from one end thereof to the other, heating the tube throughout its entire length in order to maintain said mixture in the gaseous phase at a first temperature, said mixture being in contact with substantially all the inner surface of said tube, and moving a heat zone at a second temperature in the direction along said tube from said other end thereof to said one end thereof, said first temperature being below the temperature at which deposition of metal from said heat decomposable metal compound occurs, said second temperature ranging from 650 to 1050 C. in order to deposit said molybdenum on the inner surface of said tube.

4. A process for coating the inside of an elongated tube, said process comprising the steps of directing a mixture of molybdenum carbonyl vapor and hydrogen through said tube from one end thereof to the other, heating said tube to a first temperature throughout substantially its entire length in order to maintain said mixture in the gaseous phase at a predetermined temperature, said mixture being in contact with substantially all the inner surface of said tube, and moving a heat zone at a second temperature in the direction along said tube from said other end thereof to said one end thereof, said heat zone having a temperature ranging from 650 to 1050 C. in order to deposit said molybdenum on the inner surface of said tube, said molybdenum carbonyl being initially at a temperature of C., said hydrogen being at approximately five times a pressure of said molybdenum carbonyl, said temperature throughout said tube being approximately 90 C., the molar ratio of said vapor being 10% molybdenum and 90% hydrogen, the total pressure within said tube of said mixture ranging from .5 to 25 mm. Hg.

5. An apparatus for depositing a metallic coating on the inner surface of an elongated tube, said apparatus comprising a first means for introducing gaseous decomposable metal compound to one end of said tube and for exhausting the other end of said tube, second means extending throughout the length of said tube for generating an extended heat zone in order to maintain said vapor at a predetermined first temperature while flowing within said tube, third means extending within a restricted section of said length for generating a restricted heat zone within said tube at a predetermined second temperature said second temperature being above said first temperature, and fourth means for driving said .third means in the direction along said tube from said; other end to said one end at predetermined speed, said second means enveloping said tube throughout its length, said third means enveloping said tube within a restricted section.

References Cited in the file of this patent UNITED STATES PATENTS Hill Feb. 26, 1957 Hanlet Mar. 31, 1959 

1. A PROCESS FOR COATING THE INSIDE OF AN ELONGATED TUBE SECTION, SAID PROCESS COMPRISING THE STEPS OF DIRECT ING A MIXTURE OF A HEAT DECOMPOSABLE GASEOUS METAL COMPOUND AND AN AUXILIARY GAS THROUGH SAID TUBE FROM ONE END THEREOF TO THE OTHER, HEATING THE ENTIRE INTERIOR OF SAID TUBE SECTION IN ORDER TO MAINTAIN SAID MIXTURE IN THE GASEOUS PHASE AT A PREDETERMINED TEMPERATURE, SAID MIXTURE BEING IN CONTACT WITH SUBSTANTIALLY ALL OF THE INNER SURFACE OF SAID TUBE SECTION, AND MOVING A HEAT ZONE IN THE DIRECTION ALONG SAID TUBE FROM SAID OTHER END THEREOF TO SAID ONE END THEREOF, SAID HEAT ZONE GENERATING A TEMPERATURE ABOVE THE TEMPERATURE AT WHICH SAID DECOMPOSSABLE METAL COMPOUND DECOMPOSES. 